The Zeta system utilizes a proprietary 3D finite element
analysis (FEA) model in combination with highly accurate
measurements from fiber optic gauges. This approach enables
accurate modeling of changing stress levels across the entire
riser/wellhead lubricator intervention stack. The system can be
used for pre-job modeling to optimize and verify the safety
margin of the job design. It can also be used in a real-time
mode in the field, to monitor and issue a warning when stresses
are approaching unsafe limits.
Pre-Job Modeling - Probability of exceeding pre-set safety
limits during the operation
- Need for additional intervention stack
supports and their location
- Stress changes as a result of stack
loading changes
- Maximum stress location
- Weight required to buckle the
stack
- Stack vibration frequency
- Optimized rig-up configuration
| Field Monitoring - Monitor intervention stack stress
levels
- Impact of changing surface, downhole,
and/or offshore field conditions
- Suspend operations if maximum stresses
approach unsafe limits
- Resume safe operations following
remediation of problem
| WHY (ZETA) IS NEEDED Zeta was developed due to potential safety
concerns associated with the use of longer
and more complex intervention stacks. These
tall stacks are more susceptible to bending
excitation forces from crane, production
riser, and platform movements. At present, a
judgment call (based on little or no hard
data) is made regarding how much lubricator
sway or wellhead movement is acceptable, when
to add supports, or even when to halt
operations due to safety concerns. Motion
associated with TLP's and Spars only compound
this problem. The Zeta Safety System
eliminates guesswork and provides a tool for
optimal rig-up configuration. EQUIPMENT The Zeta Safety System is comprised of two
basic components, the Zeta Model and the Zeta
Gauge. | (Zeta) Gauge - 2' lubricator spool built to API
requirements
- Uses fiber-optic strain gauges to
measure
- Axial force
- Internal pressure
- Bending moment (left and right)
- Bending moment (forward and
backward)
- Calculates Von Mises stress in the
gauge
- Displays force, pressure, moment and
stress values
- Communications with the Model software
in real-time
- No electricity to the gauge - no
certification issues
- Fiber optic gauges are very stable -
remains calibrated
|
 | Zeta Model - Used during job design to ensure safe
stack design
- Models entire wellhead/lubricator stack
with its supports and applied loads
- Calculates:
- Displacement (motion) of the stack
- Von Mises stresses in the stack
components
- Vibration frequency of the stack
- String weight required to buckle or
yield the stack
- Static or dynamic loading in the guy
wires or support structure
- Real-time input from the Gauge can be
used to determine maximum stresses in the
stack
- Warning when pre-set stress levels are
exceeded
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